346 White — Specific Heats of Silicates and Platinum. 



Summary. 



1. For determining the specific lieats of silicates up to 1500° 

 C. the method of mixtures, in which the heated substance and 

 containing crucible are dropped from a furnace into a calori- 

 meter at room temperature, was selected as the most accurate. 



2. The chief source of error is in the lack of uniformity in 

 the furnace temperature. This has been diminished in some 

 cases by the use of special forms of furnace. 



3. The error introduced in the process of transferring from 

 the furnace to the calorimeter is negligible. An electrical 

 method of releasing the crucible greatly reduces the time 

 required, and preliminary determinations made with the con- 

 taining crucible alone eliminate what heat loss there is. 



4. All temperatures, including that of the calorimeter, were 

 read by thermoelements. By this means rapidity and simplicity 

 of manipulation were secured. 



5. The calorimeter was completely inclosed by its water 

 jacket. An unusually large temperature rise (sometimes 23°) 

 was successfully employed to increase accuracy. 



6. Some simple ways of treating specific heats mathemati- 

 cally are given. 



7. A consideration of the various sources of error indicates 

 for the mean specific heats a final accuracy of better than 0*5 

 per cent at most temperatures. The true specific heats, 

 derived from these, are less accurate. 



Silicate specific heats show a considerable increase with 

 temperature up to 700°, followed by a tendency to diminish 

 at higher temperatures. 



Geophysical Laboratory, 



Carnegie Institution of Washington, 



Washington, D. C, July 15, 1909. 



